Method and apparatus for the recovery of latent heat of fusion



fg. 2. nf/l Hea/ Pump R. W. SHADE Filed Dec.

OF' LATENT HEAT OF FUSION METHOD AND APPARATUS FOR THE RECOVERY Aug. 22,1961 United States Patent O 2,996,394 METHOD AND APPARATUS FOR THERECOVERY OF LATENT HEAT OF FUSION Ray W. Shade, Ballston Lake, N.Y.,assignor to General Electric Company, a corporation of New York FiledDec. 13, 1956, Ser. No. 628,134 8 Claims. (Cl. 62-59) This inventionrelates to a heat storage system and, in particular, to the recovery ofthe stored heat, i.e., latent heat of fusion of a given medium, and thetransfer of this heat to a fluid by heat exchange methods.

The problem of recovering stored energy has long been a difficult one,and as yet, not fully solved in the most practical and eflicient manner.A variety of solutions to this problem has been advanced which generallyrelates to the utilization of latent heat accompanying a phase change,such as liberation of latent heat of fusion of a liquid whensolidifying, for example, water freezing to ice. An apparatus employingthis process generally includes a container for the liquid mediumundergoing a phase change, and a second liquid passing in heat exchangerelationship with or through the container by the use of coils, tubes,and the like heat excange apparatus. One of the disadvantages of such asystem is the difliculty of obtaining a high heat transfer coelcientbetween the stagnant solidifying material and the circulating liquid;therefore, resort is usually made to either very large heat exchangesurfaces and/or a choice of liquids having a very high temperaturedifferential between the one in the solid state and the other as thecirculating liquid. A further disadvantage of the aforementioned systemis that the rate of heat transfer decreases quite rapidly with theformation of ice on the heat exchanger structure, resulting in a lowtransfer rate with a relatively large amount of liquid remaining whoselatent heat of fusion is impracticable to recover.

Accordingly, it is an object of this invention to provide a highcoefficient of heat transfer between the fluid components of a heatstorage system.

It is another object of this invention to provide for the employment ofdluids having a relatively small temperature differential between theone circulating and the other as a solid in a heating and coolingsystem.

It is a further object of this invention to provide a substantiallystable rate of heat transfer between the working components of a heatrecovery system in heat exchange relationship.

It is a still further object of this invention to provide a small andefficient heat storage system employing essentially irnmiscible liquidsof different densities and employed as an auxiliary heating system.

Briefly stated, in accordance with one aspect of this invention, heatexchange structure between the liquids of a liquid medium in a heatstorage system is substantially eliminated and replaced by a process ofintermingling liquids having different densities and essentiallyiminiscible characteristics one with the other, in direct contact. Oneof the liquids undergoes a change of state and the accompanyingliberation of the latent heat of fusion is readily absorbed by theremaining liquid which is employed to provide heat.

These and various other features and advantages of this invention willbe better understood from the following description taken in conjunctionwith the accompanying drawings, in which:

FIG. l is an illustration of one embodiment of a heat storage system;

FIG. 2 discloses a second embodiment of this invention; and

ice

FIG. 3 discloses a non-circulating modification of this invention.

FIG. 4 is a schematic representation of a heat pump or primary heatingdevice which is connected to its evaporator, or the heat exchanger, ofFIG. l.

Referring now to FIG. l, a container or column 1 is provided in whichthe mixing of fluids takes place. These fluids are generally chosen fromthose having different densities and immiscible characteristics, inorder that, after mixing, separation may take place rapidly withoutadditional aid from external sources, thus permitting the circulation ofone of the fluids without undue entrainrnent of the other. It is to beunderstood that many fluids exist which have different densities andimmiscibility characteristics; however, for explanatory purposes, awater-oil mixture will be utilized to disclose a working embodiment ofthis invention. The column l which may be insulated, as shown at 2, ispartly filled with water 3. Thereafter, oil, at a temperature below thefreezing point of water, is introduced below the water surface, asindicated by entrance conduit 4 and spray nozzle S to spray the oil intothe water 3i. The nozzle 5i is designed to give maximum dispersion andturbulence of the oil in the water, and this dispersion of the oil,together with the turbulence generated by the nozzle 5, provides a highrate of heat transfer from the water to the oil, with a resultantcooling of the Water and ice particle formation. A high rate of heattransfer is realized from the continuous contact between the water andthe oil. The phase change from water to ice liberates latent heat offusion which is then absorbed by the oil. The small ice particles thusformed settle in a layer 6 at the upper water level in column 1, and thewarmed oil 7 rises to above the water and ice layer. The oil, now at anincreased temperature, is circulated by means of a pump S from thecolumn 1 to heat exchanger 9 where heat is removed from the oil. One ofthe methods which may be employed to remove the heat from thecirculating oil 7 is the use of a circulating fluid entering the heatexchanger 9 at 1G and exiting at 11. The removed heat may then beutilized in various applications, for example, to be applied to theevaporator of the domestic type heat pump 20 (FIG. 4) during periods ofextremely cool weather, a process which results in the same reaction inthe heat pump 20 as an increase in the ambient air temperature. However,in the latter example the heat pump evaporator may be combined with theheat exchanger 9 and in this instance may be referred to as heat pumpevaporator 9. FIG. 4 is then merely an illustration of this latterexample where the heat pump 20 is connected to its evaporator by meansof inlet 10 and outlet 11 to its evaporator 9*. It is thus understoodthat the latent heat of fusion recovery system becomes an auxiliaryheating system or heat source to a primary heating system, i.e., theheat pump, and of course the efficiency of the heat pump is thus greatlyincreased. The oil leaving the heat exchanger 9, at a reducedtemperature, is returned to inlet 4 in column ll for a repeat of theprocess heretofore described.

lf perhaps additional mixing and turbulence is desired in container l,any of the well known mixing or agitating devices may be employed inthis invention. Such a device may take the form of a mixing impeller 12connected to a shaft 13 which is arranged to be rotated by an externaldrive, not shown. However, since additional mixing is but a matter ofexpedience, it forms no part of this invention.

One of the advantages to be derived from the introduction of oil belowthe water surface includes the extended time interval of the oil risingthrough the water for more favorable and increased heat transfer. It

should also be evident that the turbulent action prevents or minimizessub-cooling, and therefore gives a steady rate of heat transfercommencing at approximately 32 F.

The formation of ice particles continues until such time assubstantially all the latent heat of fusion of the water has beenabsorbed and the Water becomes a rather dense sludge or ice-Watermixture in the bottom of column 1. As an alternative to stopping theoperation under these circumstances, heat may be applied to the unit forice melting or heat supply purposes. Various types of additional heatingmeans may be employed to supply heat in this invention includingelectrical resistance coils, mechanical heat exchange structure, or heatfrom ambient conditions. In FIG. l there is shown a heat exchanger coil14 adjacent the ice layer 6. One or more of these coils may bepositioned in the Water 3, the ice layer 6, or in the oil 7, theparticular location being a function of the anticipated operation.

Unit operation may also be of the intermittent variety wherein only partof the water is frozen and, in the case of heat pump evaporatorapplication, no further heat is necessary. During these periods ofinactivity heat may be obtained from the heat pump, when an excess isavailable, to be supplied to the unit for ice melting, thus assuring afull supply of heat (or water) for the succeeding operating period. Itis, of course, obvious that the system is reversible in the followingsense. Assume that container 1 is in the condition as illustrated inFIG. l where ice is present. Under these conditions the heat pumpevaporator 9 is to be cooled instead of heated as previously described.Pump 8 is operated to pump oil through the evaporator to take up heat.The warmed oil is then introduced through nozzle 5 and melts the ice inthe water 3i. Melting of the ice provides transfer of latent heat offusion from the melting ice to the oil.

In order to conserve heat, many refinements may be incorporated in thisinvention. Specifically, the pump and drive may be of the submergedtype, and the heat of operation absorbed by the oil or water. Further,

a part of the container 1 may be mounted in heat exchange relationshipwith other heat generating devices in the domestic type heat pump orother such device to which this invention may be applied.

FIG. 1 which illustrates one preferred embodiment of this invention, maybe modified without departing from the scope of this invention, to analternate operation wherein the water may be sprayed into the oil forparticle freezing therein and a settling out. The choice of the sprayingmedium, however, will be largely determined by the operating factors,particularly the specific application of this invention.

A water spray system. of the type described is illustrated in FIG. 2wherein water from any suitable source, such as a domestic home supply,is introduced into oil 7 through conduit 16 and spray nozzle 5. Thefreezing ice particles release latent heat of fusion to the oil andsettle to the ice layer 6 at the water-oil boundary. Water, and in somecases a water and ice mixture, is removed from the container 1 throughconduit 17 by a pump 18, which is capable of pumping, if necessary, asludge of ice and water.

The water spray method presents a dual configuration. In one, the closedsystem, the withdrawn water may be recirculated into the container 1with the unit reaching a shut-down point when substantially all thewater is frozen and no external heat is supplied. In the otherconfiguration, the open system, water may be, as necessary, continuouslysupplied to the container 1 and the resulting sludge continually pumpedto a suitable disposal, such as a sewer system, and the like.

This latter configuration entails some small loss of oil over a periodof time and necessitates the addition of a small quantity of make-up oilwhen needed. On the other hand, the system not only eliminates therequirement of equipment and energy for the melting of the ice, but alsomay eliminate or reduce the capacity requirement of the pump to pumpwater into column 1.

A modified form of this invention may eliminate circulating the oilexteriorly of the container 1. Referring now to FIG. 3 there is shownthe container 1 with oil 7 and water 3 therein in separate layers. Aheat exchanger coil 19 is positioned within the oil layer to circulate afluid of a lower temperature than the freezing point of the water. Thisprocess cools the oil surrounding the heat exchanger and produces somecirculation of the oil near the water-oil division. In so circulating,the cold oil 7 is brought in contact with the water 3 which freezes andgives up latent heat of fusion to the oil, which is turn transfers heatto the circulating fluid in the heat exchanger coil 19.

Heat exchanger coil 19 is preferably mounted in the oil to prevent iceformation thereon and the resultant reduction in rate of heat exchange.Additionally, it may be desirable to provide means for generatingturbulence to prevent ice formation in a relatively large body, and forsuch purpose various devices may be employed including the impelleragitator 12 as illustrated in FIGS. l and 2. Furthermore, heat may beadded to the container 1 by heat exchanger coil 19', or other heatingarrangements as described for FIGS. l and 2.

This invention as described relates to the recovery of latent heat offusion and utilizes a water-oil mixture for explanatory purposes. It isto be understood, however, that this invention may utilize variouscombinations of liquids including also solutions of certain materials,for example, disodium phosphate with liquids which will solidify atpredetermined temperatures to liberate latent heat of fusion. Thisliberation of latent heat of fusion may be carried on at atmosphericpressure by venting the container 1 as at 15 or, alternatively, theprocess may be carried out at pressures below as well as aboveatmospheric.

While other modifications of this invention and variations of apparatuswhich may be employed within the scope of this invention have not beendescribed, the invention is intended to include all such as may beembraced within the following claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. in a closed cycle latent heat recovery system employing a containerhaving therein a liquid medium, said liquid medium comprising a solutionof disodium phosphate and water which will precipitate solid disodiumphosphate at a predetermined temperature, the method which comprises,introducing into said solution a liquid at a temperature below thesolidifying temperature of the disodium phosphate to cause solidificatonthereof and a concurrent release of latent heat of fusion to saidliquid, maintaining the said liquid and the said solution in separatelayers in said container, circulating the said liquid from itsrespective layer in said container to a heat exchanger for a withdrawalof heat therefrom, utilizing the heat obtained from said heat exchanger,returning said liquid to the said solution, and adding heat to saidsolution in said container to dissolve the solid disodium phosphate.

2. The invention as claimed in claim 1 wherein said introduced liquid isoil.

3. The invention as claimed in claim 1 wherein said introduced liquid iswater.

4. An apparatus utilizing latent heat of fusion which comprises incombination, a primary heating device having a heat exchangeroperatively connected thereto to increase the eliiciency thereof, andauxiliary heating means to add heat to said heat exchanger, said heatingmeans comprising a container operatively connected to said heatexchanger, said container containing a liquid medium therein, saidliquid medium having a component of a higher solidication temperaturethan the remainder of said medium, means circulating the remainder tosaid heat exchanger for cooling of the remainder below thesolidification temperature of said component, means intermingling saidcooled remainder in said component in heat exchange re1ationship\.tocause particle soliditication of said component and a concurrent releaseof latent heat of fusion to said remainder, said recirculating meansrecirculating said remainder through said heat exchanger to provide heatthereto prior to a recontacting with said component, and means to meltsaid particles in said container.

5. The invention as claimed in claim 4 wherein said heating device is aheat pump and said heat exchanger is the evaporator for said heat pump.

6. The invention as claimed in claim 4 wherein said liquid mediumcomprises a pair of liquids having different densities and emissibilitycharacteristics.

7. An apparatus utilizing latent heat of fusion which comprises incombination, a heat pump including7 an evaporator operatively connectedthereto, and a closed cycle system to supply heat to and remove heatfrom said evaporator, said system comprising a container operativelyconnected to said evaporator, said container having liquid mediumtherein, said liquid medium having a component which will solidify ahigher temperature than the remainder of said medium, means circulatingsaid remainder to said evaporator to cool said remainder below thesolidiication temperature of said component, means introducing the saidcooled remainder directly into said component in heat exchangerelationship to cause particle solidication of said component and aconcurrent release of latent heat of fusion to said remainder, saidcirculating means recirculating said remainder to said evaporator forwithdrawal of heat from said remainder for return of said remainder tosaid component, and means to melt said particles in said container.

8. A method of utilizing latent heat of fusion as an auxiliary heatingsystem to supply heat to a primary heating apparatus having a heatexchanger to increase the efliciency of said primary heating apparatuscomprising, utilizing a closed cycle latent heat of fusion recoverysystem with said heat exchanger which includes, employing in said closedcycle latent heat recovery system a liquid medium characterized byhaving a component which will solidify at a higher temperature than theremainder of said medium, circulating the said remainder of said liquidmedium through said heat exchanger for release of heat therein,intermingling the said cooled remainder with said component to causeparticle solidication of said component and concurrent release of latentheat of fusion to said remainder, and circulating said remainder throughsaid heat exchanger for release of latent heat therein, and providingmeans to melt said particles in said container.

l References Cited in the Ile of this patent UNITED STATES PATENTS523,412 Scheler f July 24, 1894 1,969,187 Schutt Aug. 7, 1934 2,507,632Hickman May 16, 1950 2,613,513 Shields Oct. 14, 1952 2,631,835 Jones lMar. 17, 1953 2,666,304 Ahrel Jan. 19, 1954 2,764,488 Slattery Sept. 25,1956 2,778,607 Leoni Ian. 22, 1957 2,886,603 Shelton r May 12, 1959FOREIGN PATENTS 537,450 France May 23, 1922 UNITED STATESV PATENT OFFICECERTIFICATE OF CORRECTION Patent, Noe. 2996894 August 22 1961 Ray W,Shade C It is hereby certified that err-or appears in the above numberedpatent requiring correction and that the said Letters Patent should readas corrected below.

` Column 3Y line 359 for' Nirom the melting ice to the oil-Uv read fromthe oil to the melting ice Signed and sealed lthis 12th day of June1962.,

, (SEAL) Attest:

4xemuzsfr w. swIDER` DAVID L. LADD Attesting Officer Commissioner ofPatents

